UTC-IC UC3656G-AF5-R

UNISONIC TECHNOLOGIES CO., LTD
UC3656
Preliminary
CMOS IC
1MHz,800mA SYNCHRONOUS
BUCK CONTROLLER
„
DESCRIPTION
The UTC UC3656 is a synchronous buck controller for a DC/DC
converter optimized for high-performance microprocessor applications.
It is configured with current mode for excellent line and load
transient response. At 1MHz operation frequency, the use of small
surface mount inductor and capacitor is enabled. The built-in
synchronous switch saves the use of an external Schottky diode and
increases efficiency.
The UTC UC3656 is a low-noise synchronous step-down DC/DC
converter that is ideally suited for systems requiring supplies from a
1-cell Li-ion battery or from a 3-cell to 4-cell NiCd, NiMH, or alkaline
battery.
The UTC UC3656 is generally applied in power supply for portable
devices and USB-based power system.
„
FEATURES
* High Efficiency (95%) Possible
* Input Voltage Range: 2.5V ~ 5.5V
* Schottky Diode is Saved
* Output Current: 800mA (@5V Input 3.3V Output)
* 1.0MHz Oscillation Frequency
* Internal ON/OFF
* 100% Duty Cycle Allows Low Dropout Operation
* Stand-by Current: 1μA (Max.)
„
ORDERING INFORMATION
Ordering Number
UC3656G-AF5-R
„
Package
SOT-25
Packing
Tape Reel
MARKING
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Copyright © 2010 Unisonic Technologies Co., Ltd
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UC3656
Preliminary
„
PIN CONFIGURATION
„
PIN DESCRIPTION
PIN NO.
1
2
3
4
5
PIN NAME
Run
GND
SW
VIN
FB
CMOS IC
DESCRIPTION
ON/OFF Control
Power Ground
Switch Node Connection to Inductor
Power Supply
Output Feedback
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UC3656
„
Preliminary
CMOS IC
BLOCK DIAGRAM
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UC3656
„
Preliminary
CMOS IC
ABSOLUTE MAXIMUM RATING
PARAMETER
Power Supply Voltage
RATINGS
UNIT
-0.3 ~ +6.0
V
RUN,FB
-0.3 ~ VIN
V
Input Pin Voltage
SW
-0.3 ~ VIN +0.3
V
P-Channel Switch Source Current (DC)
1000
mA
N-Channel Switch Sink Current (DC)
1000
mA
Peak SW Sink and Source Current
1.5
A
Ambient Operating Temperature
TOPR
-35 ~ +85
°C
Storage Temperature
TSTG
-55 ~ +150
°C
Note: Absolute maximum ratings are those values beyond which the device could be permanently damaged.
Absolute maximum ratings are stress ratings only and functional device operation is not implied.
„
RECOMMENDED OPERATING CONDITIONS
PARAMETER
Power Supply Voltage
Junction Temperature
Operating Junction Temperature
„
SYMBOL
VIN
TJ
TJ
RATINGS
2.5 ~ 5.5
+150
-20 ~ +85
UNIT
V
°C
°C
SYMBOL
θJA
RATINGS
165
UNIT
°C/W
THERMAL DATA
PARAMETER
Junction to Ambient
„
SYMBOL
VSS
VIN
VIN
ELECTRICAL CHARACTERISTICS (VIN=3.6V, TA=25°C, unless otherwise specified.)
PARAMETER
SYMBOL
TEST CONDITIONS
Input Supply Range
VIN
Quiescent Current (Note)
IS
FB=0.8V, ILOAD=0A, Active Mode
Current In Standby Mode
IST
RUN=0V, VIN=5.5V
Feedback Voltage
VFB
TA=-20°C ~ +85°C
Feedback Voltage Line-Regulation
VFB-LINE VCC=2.5V ~ 5.5V
Feedback Variation with Temperature
TA=-20°C ~ +85°C
Feedback Current
IFB
Peak Inductor Current (Note)
IPK
VIN=5V, VOUT=3.3V
Maximum Output Current (Note)
IO
VIN=5V±5%, VOUT=3.3V, L=4.7µH
fOSC1
FB=0.8V
Oscillator Frequency
fOSC2
FB=0V
RDS(ON) of P-Channel MOSFET
RPFET ISW =600mA
RDS(ON) of N-Channel MOSFET
RNFET ISW =-600mA
SW Leakage Current
ILSW
RUN=0V,SW=0Vor 5V,VIN=5V
RUN Threshold
VRUN
RUN Leakage Current
IRUN
ΔI
( VIN − VOUT ) × t ON
Note: IPK = IO +
= IO +
2
2×L
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MIN
2.5
TYP
0.588
300
0.5
0.6
0.1
0.5
1.10
1.25
0.8
1.0
200
0.4
0.35
±0.1
1.0
±0.1
0.3
MAX UNIT
5.5
V
µA
1
µA
0.612
V
0.5
%
1.0
%
±200
nA
1.50
A
800
mA
1.2
MHZ
KHZ
0.5
Ω
0.45
Ω
±1
µA
1.5
V
±1
µA
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UC3656
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Preliminary
CMOS IC
TYPICAL APPLICATION CIRCUIT
L1
4.7μF
VIN
5.0V
4.7μF
VOUT
1.8V/800mA
SW
VIN
SW
47pF
UC3656
R2
10μF
FB
RUN
R1
1M
GND
Figure 1
L1
4.7μF
VIN
5.0V
4.7μF
VOUT
3.3V/800mA
SW
VIN
SW
47pF
UC3656
R2
10μF
FB
RUN
R1
1M
GND
Figure 2
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UC3656
Preliminary
CMOS IC
„
APPLICATION INFORMATION
Capacitor Selection
Proper selection of capacitors using the UTC UC3656 plays a critical role for system performance. The source
current of the top MOSFET is square wave of duty cycle in a continuous mode.
The input capacitor is generally used to provide a low impedance loop for the edges of pulsed current drawn by
the UTC UC3656. A load step at the output can induce ringing at the input VIN. This ringing can couple to the output
and be mistaken as loop instability. Increasing the capacitance of the input capacitor can great improve the
oscillation. A typical value is 4.7~ 22μF ceramic (X5R or X7R), POSCAP or Aluminum Polymer. With these
capacitors, better high frequency bypassing is achieved; resistive losses are thus reduced by their low ESR for
higher efficiency. Moreover, the input capacitor RMS current changes with the input voltage and the output voltage.
The maximum RMS current in the input capacitor can be expressed in the following formula:
IRMS = IOMAX
V
VO
(1 − O )
VIN
VIN
The output capacitor depends upon the suitable ripple voltage. Low ripple voltage corresponds to lower effective
series resistance (ESR).
1
)
The output ripple voltage can be calculated by: ΔVOUT ≅ ΔIL (ESR +
8fCOUT
The formula as follows shows the output capacitor RMS ripple current: IRMS =
1
2 3
VOUT × ( VIN − VOUT )
L × f × VIN
For the UTC UC3656, X5R or X7R dielectric formulations have the priority in choosing the input and output
ceramic capacitors. This is because these dielectrics provide the best temperature and voltage characteristics of all
the ceramics for a given value and size.
Inductor Selection
Selecting an optimum inductor is dependent upon the expected ripple current and large value inductors lower
ripple current and small value inductors result in higher ripple current. In addition, the losses associated with the
DCR and its effect on the total converter efficiency should be taken consideration.
The inductor is also chosen to limit the ripple current to some pre-fixed value, approx. 20 ~ 40% (TYP.) of the
full load current at the maximum input voltage.
The inductance value can be calculated in the following equation:
ΔIL = 0.2 ~ 0.4 × IOUT(MAX)
L=
VOUT
V
(1 − OUT )
f × ΔIL
VIN
Adjustable Output Voltage
A resistive divider adjusts the output voltage of the UTC UC3656, which divides a 0.6V reference voltage at FB
pin. The output voltage can be obtained by the equation as follows:
VOUT = 0.6V × (1 +
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R1
)
R2
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UC3656
Preliminary
CMOS IC
UTC assumes no responsibility for equipment failures that result from using products at values that
exceed, even momentarily, rated values (such as maximum ratings, operating condition ranges, or
other parameters) listed in products specifications of any and all UTC products described or contained
herein. UTC products are not designed for use in life support appliances, devices or systems where
malfunction of these products can be reasonably expected to result in personal injury. Reproduction in
whole or in part is prohibited without the prior written consent of the copyright owner. The information
presented in this document does not form part of any quotation or contract, is believed to be accurate
and reliable and may be changed without notice.
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